Process of fixing nitrogen



Jan. 9, 1923.

K: P. McELROY.

PROCESS OF FIXING NITROGEN.

ORIGINAL FILED MAY15,1919.

' terials.

Patented than. 9, 31323.

irri r i a we d l lift! 4&3 LL14 to;

ti. t \Juzao KJI'LRL R, IBICELRGY, OF WASHINGTUN, DISTRICT OF COLUT/IBIAASSIGNOB TO FEBRO CHEMICALS INQ, OF WASHINGTON, DISTRICT OF COLUIKBIA. ACORPOHA'IION OF DELA'WARE.

EROCESS OF FIXING NITROGEN.

Application filed may 15, 1319, Serial No. 297,294. Renewed Jiine 7,1922; Serial No. 566,547.

Bait known that 1, Kim, 1. l /lCELkUY, a citizen of the Unitedtltates,residing' at VJashingtornin the District of olumbia.

' have invented certain new and useful improvements in Processes ofFixing Nitrogen, of which the following is a specificatiOH;

p This. invention relates to processes of fixing nitrogen; and itcomprises amethod of producing cyanids or ammonia wherein an alkalicarbonate in a molten state is percolated through or flowed over carbonand iron or votheriron group metal in counter-- current to a stream ofhot produfi'er gas. thereby producing molten rvauid and an cnriched allas more fully hereinafter set forth and as claimed.

1 'Asis well known. potassiumrcarbonate imingled with carbon and ironturnings on exposure to the air at a temperature around a red heatreadilv goes over into potassium "cyanid at thc expense ol theatmospheric nitrogen. The same action takes place in the absence of theiron. but only at higher temperatures. In the presence oi iron. about()$)l)ll C. sullice. in addition to cyanid, the action produces carbonmon- 0xid. it is quite endothermic. absorbing much heat. The reactionsare the same. if .producer gas besubstitutcd for air or if sodiumcarbonate or barium carbonate be substituted for potassium carlmnatc.Many propositions have been made to utilize the action for commercialpurposes: and in soino cases with a degree of success. 'lhcrc arehowever many incident dilliculties. in part these are the usual troublesin heatin a pervious or granular mixture undergoing heat-absorbingreactions in a retort of anyjsize without excessive heating ofthereltort walls. Its-l have Found. this diliiculty may be in large partovercome by the expedient employed by Castner in malting sodium, viz,using" the iron as balls or bodies of substantial size capable oi car-'rying heatthroughout the mix. Another diiiiculty lies in the characterof the ma- Both potassium carl'ionate' and sodium carbonatemelt attemperatures a little over 800 C. Both give thinly l'luid liquidsflowing readily and exhibiting the ordinary capillary actions so that itis hard to preserve admixtures of carbonates with other n'mtcrials atmelting: temperatiu'es. At temperatures below 800 cyanidatiou isrelatively slow and at temperatures niutlr above. carbomitc tends toliquatc out of the mass. find. as stated. it is diliicuit to preventhigh temperatures next the wall with rctorts of any size. lihpiation mayto some extent be prevented by increasing the amount oi iron or charcoalin the mix; but this introduces new dillicultics it the cyanided mass beafterwards leached to recover cyanid. .licading without t'ormalion oii'errocyanids is diliirult in any case. l urther. at temperatures muchabove l cyanids have a tendency to volatilize.

in the present invention. advantage is taken oi the stated properties.melting being utilized instead ot' avoided. 'lhc reaction mixture-islccpt at a sutlicicnt temperature to prodi'ice free fluidity of theparticular carbonate used. and the carbonate in a mo ten torn! isallowed to flow through or orcr iron and carbon as a thin layer. flowingin contact with producer gas. suniiug a horizontal or somewhat inclinedretort to be used. carbonate fed at one end and omcrgcs as cyanid at theother. A- siniple liltcr of iron wire at the. unit end holds back ironand carbon and prevents thcir groin; forward with the cyan'id. A.relatively purc product. requiring no leach in; is thus obtained. litmay flowinto molds to l'orm sticks or balls as it emerges. using anysuitable type of molding nnn-hinc. As a source oi nitrogen I useproducer gas flowing; in conntcrcurrcnl twl'he molten carbonate. Tho gasis improved in quality by the operation to the extent that it is freedoi nitrogen and is enriched in carbon-mimoxid by the reaction. Carbonmay or may not be supplied with the arbonate. By catalytic action ofiron on carbon mom oxid. the gas itsellwillsupply ('ttl.l)(')ll. Or a.little oil or other: hydrocarlmn may be ted in with. the producer (hisfrom bituminous coal carrying carbon in the form (it distillation gasessusceptible of use; but should; for the sake, ol carryingheat. bepreheated. Ordinarily l find it better toadd carbon to the reaction zoneand use n'odurer gas made "from fixed fuel (coke or ai'ithracite) in ahigh tcnmerature producer (what is known as a shinning pro-- ducer) asthis enables me to take into the system much or all of the heatrequired. lresuming the gas to he at 12300" or ltoo the excess of heatabove, say. $10 is available for compensating the endothermic action inthe formation oi cyanids. Such a gas will carry about the theoreticalproportion of (T0 (about 33 per cent) prior to entering the apparatusand will be much richer on leaving: the extent of the enrichment ofcourse tlepcndingfiipon the way the operation is conducted.

in adding carbon. I tind it particularly advantageous to use charcoal inwheat or beau size. supplying this charcoal through the gas outlet oi"the apparatus. in so doin any cyanid 't'umes which may escape with thegas are caught by the charcoal and rcturned: the charcoal acting as agas litter. or, rather. an adsorbent purifying agent.

The operation may he conducted in any type of ordinary iron retort ortubular heating device; and. where a slightly enriched producer gas is aprimary object. all the heat may he conveyed by the gas. a rapid streamflowing over the carbonate. ()rdinarily however t supply some outsideheat as well. it' only to prevent radiation losses: and l lind it betterto use a flat. basin-like horizontal or slightly inclined iron platewith heating furnace or flame chamber he-' neath and carrying adetachable iron top. heat insulated by tire brick. magnesia. kieselguhror other suitable material. This enables ready inspection and repair."he

bottom plate may he in one or more seetious: and may he of cast iron ormade by Hanging up a steel or iron plate. It may he corrugated or ribbedto give circuitous How of carbonate: and the ribbing may give all theiron surl'ace necessary. llowcver. it is ordinarily simpler to have aflat bottom and provide for contact and catalysis by means of pieces ofiron. such as bars. pipe sections, wire. nails. or the like. 01'. lumpsof iron ore (which are at once reduced to spongy iron) may hedistributed over the bottom with an iron grid. shaped for the desiredtype of flow. to hold them in place.

Whatever the way adopted. the object is to provide iron so distributedin the path ol' the current ol' molten carbonate as notto interrupt theHow unduly. (hat-coal. soot. etc.. in the required amount is fed inwith. or in addition to.'tlie feed or carbonate. and flows forward withthe carbonate. damming up more or less on the iron. till it disappears.It ash constituents accumulate on the hearth. the apparatus may hecleaned by a flow of carbonate without carbon over the hearth to a time.letroleum coke or other ashless forms of carbon may he used and allow alonger period of run without cleaning. Anthracite. coke, breeze, etc..necessitate frequent eleaning. By adding a little natural gas or sprayedoil with the gas,.carhon is For nitrogen fixation. a mixture of sodiumand potassium carbonates hasadvantages over either singly since it meltsat a lower temperature and flows" better. I

In making cyanid. the molten product dolivered a l'ter solidification(which may be in th usual molds) is directly marketable for mostpurposes. it may of course be puri tied in the usual ways. Where fixednitrogen is the product desired. the hot molten cyanid may he deliveredinto a steam (ham-- her or atomized with steam to convert the cyanidinto ammonia and recover the alkali in oxidized form. it the temperaturein this chamber is kept at. say, tim Q, the alkali is delivered in dryform and can be sent back to the cyaniding chamber at once.

in the accompanying illustration I have, shown. more or lessdiagrammatically, certain apparatus within the described inven tion andcapable of use in the performance ol' the described process. In thisillustration the figure is a View in vertical section, certain partsbeing in elevation. For the sake of clarity of illustration the size ofthe reaction chamber is exaggerated in comparison with the size of thegas producer.

ln this showing element 1 is'an ordinary type oi slagging gas producerprovided with tuyeres 2 for delivering cold or hot blast, advantageouslya hot blast. in securing the hot blast. air may be heated in the usualwell understood ways (not shown) by the aid of waste heat from thecyaniding apparatus. slag outlets 3. -a t'uel feeding device -.t and anoutlet 5 delivering hot gas. The temperature oi" this gas may be, 1400"C. or"

more. The cyaniding apparatus as shown consists of a long narrow hearth.6 which may he of sheet iron or cast iron or even of copper. It ismounted on the top of a tiame chamber or combustion space 1' having agas burner 8 at one end and outlet 9' torprodnets of combustion at theother end. The hearth of the cyaniding chamber is virtually a top forthis tlaine chan'iber. As shown, the eyaniding chamber has a top It)which may he of iron and heat insulated by layer it of bricks.magnesia,etc. Passing throi'igh the top or cover is a charcoal columnand gas purifier 12. At its base this coluiunis closed by plate 13,shown as somewhat The producer is provided with coned. This may be moyedup and down by stem 14: and lever 15 thereby controlling the flow ofcharcoal into the apparatus. Charcoal is supplied by bell and hopper 10entering side conduit 1?. From the charcoal column leads gas conduit 1b.is an outletwhich may be controlled by water cooled valve 20. Gas fromthis outlet may he led around by connections not shown for use in theheating chamber. Beyond the charcoal column is carbonate inlet 21 shownas of the usual type ior feeding solid materials. As shown. the hearthis some what inclined and is provided with a number of pieces of solidiron 22. It is not necessary to provide both the charcoal inlet and thealkali inlet since the alkali and carbon may be fed in through the sameinlet; but it is convenient to have separate inletsQ here the two areied'together they may be supplied in the calculated quantity of onemolecule of carbonate to four atoms of carbon. Feeding the twoseparately has the advantage of allowing the hearth to be cleaned byalkali from time to time in the manner described. While caustic alkalimay be supplied in lieu of carbonated alkali its use is not ordinarilyworth while.

In the use of the described apparatus a certain amount of carbon is fedin by opening valve 1 and deposited on the hearth. Alkali carbonate isadmitted at 21 and meltcd by the heat of the apparatus. It then flows iorward. carrying arbon with it. through a more or lesstortuous pathwayformed by the iron on the hearth and. reaches the other end oi theapparatus i ully cyanidcd. The molten cyanid iiows out through exit 221shown as provided with screen 24-. This screen operates to hold backcarbon. iron. sintered ash constituents. etc. The very hot producer gasentering through 5 gives up its heat and part oi' its nitrogen.receiving an addition to its -conicnt oi U. ll: passcs out at 18 lunchenriched. any cyanid vapors being abstracted by the charcoal in 1; Theheat required in the 7.0110, oi reaction may be furnished mainly byburner H or mainly by the hot gas coming in from in the iormcr case thegas delivered at 18 may he very rich in (t). in the latter casc. thcenrichment is not so great since the How oi gas may be relatively i'astin order to carry in the necessary num ber ol hcat units tor a givenproduction. "herc heat ol the gas is rclicd upon. burning of gas underthe hearth may be wholly omitted. int l believe it bcttcr to burn somegas at least in order to keep the ap paralius hot. in starting the useoi a burner is alwavs advisable.

'lhc catalytic inclal on the hearth may be iron in any oi' the formsstated or it may he onc oi' the other iron group metals, cobalt ornickel, lioth cobalt and nickel are gig very active catalysts infacilitating the cyanid reaction and though they are more costly thaniron yet they are not consumed in use.

The cyanid iormed may be steamed in the manner (lt. t'1ll)(*(l and theoxidized alkali metal compounds recovered and returned to the zone ofreaction at 21.

.Vhile I have shown the reaction chamber or hearth as slightly inclinedit may have a high degree oi inclination or cven be vertical. ll'ithvertical or high angle position however the interior iron must he heldin position in some way and so shaped as to give iree passage of gas inone direction and ot"carbonate holding suspended carbon in the other;and it is thcrelore better and simpler to use the somewhat inclinedhorizontal apparatus shown. it is oi ten advantageous to have the angleoi inclination somewhat greater at the carbonate end than at the cyanidend for the reason that the carbonate is rendered slower flowing and aptto dam up on the iron by the presence oi suspended carbon as it enters.

impurities from the ash of the charcoal, dust carried in by the gas(which however is mostly carbon). etc.. tend to accumulate in theapparatus and. as stated. may be re moved periodically by flushing outwith alkali. Or the apparatus may be cleaned out by taking oit' the top.in either event. the impurities removed carry alkali and though this maybe recovered in the ordinary way by leaching it is simpler to put thecleanings into the producer, ii the latter is oi the hot-gas type shown.llere the alkali is converted into cyanid vapors which pass forward withthe hot gas into the reaction chamber and add their cyanid to thatproduced therein. With a slag ot' the ordi-, naryllllIO-tllllll'lll'lfl-Sllh'tt type produced in iron i'urnaccs butlittle of this alkali will be. slaggcd oil. in the. gas producer it. isnecessary to add lime or limestone. to slag the incl ash: and ii calciumcarbonate from alkali i'actories and the like carrying some alkali beavailable, this alkali may be recovered as cyanid in the way just statedas regards the cleanings oi the reaction chamher.

ill] or other hydrocarbon material. such as natural gas may beintroduced directly into the reaction chamber by valved pipe 25 which isbest \vatcr jacketed. All the hydrocarbons tend to break up at thetemperature maintained in the reaction chamber into hydrogen. which goesforward with the gas. and carbon which for the most part, dcpositcd onthe iron, cobalt or nickel used as a catalyst for pr n'ioting the cyanidreaction, these metals being also active catalyzers of the dissociationoi hyilrocarbons. This carbon is ashless. llven where using carbon fromthis source for performing the bulk of llf) will

the cya-niclation, however, I use charcoal or some sort of porouspetroleum coke in 12 as a gas filter and pass more or less of it down onthe hearth, partly for the purpose of recox'ering the cyauid and partlyto give porous carbon on the hearth. through which the 'arbonate andcyanid may filter on their way to exit. Some or most of the carbon fromfilter 12 may be sent to the producer 1 Where its cyanidis volatilizedand returned to the reaction chambe' and its carbon utilized to produceThe use of injectedioil or hydrocarbmi gas is particularly desirablewhere spongy iron (i rbalt or nickel) is used on the hearth since itdeposits carbon in the pores in a convenient way and since the metal. isthen not so much contaminated with ash constituents of charcoal.

What I claim is v 1. lheprocess of fixing nitrogen which comprisesflowing a stream of molten alkali carbonate in countercurrent to hotproducer gas in the presence of an iron group metal and carbon. I

2. The process of fixing nitrogen which comprises establishing andvmaintaining a shallow pool of molten material in Contact.

with overlying, producer gas, feeding at all carbonate to one end ofsaid pool-and removing molten cyanicl from the other end.

3. The process of fixing nitrogen which comprises feeding alkalicarbonate and carbon into one end of a relatively shallow, ne pool ofmolten materialcontaining a solid iron group metal, passing acountercurrent of producer gas thereabove, and tapping off molten cyanidin a filtered condition from the other end of the pool.

a. The process of fixing nitrogen which comprises converting alkalicarbonate into alkali cyanid on a hearth in the presence of carbon and;iron group metal and passing the Waste gases through a carbon filter toremove vapors of cyanid.

The process of fixing nitrogen which comprises converting alkalicarbonate into alkali cyanid on a hearth in the presence of carbon andiron group metal and passing the waste gases through a carbon filter toremove vapors of cyanid, said carbon being supplied to the hearth toreturnsaid cyanicl and furnish carbon for the reaction.

6. The process of fixing-nitrogen which comprises establishing andmaintaining av relatively long pervious layer of iron group metal andcarbon, percolating alkali carbonate therethrough and passing hotproducer gas in countercurrent to the percolating liow.

7; The process of making cyanid and improving the quality of producergas which comprises passing'suc-h gas in a hot condition 'incountercurrent to a flow of alkali carbonate passing in a pathcontaining carbon and iron group inetal.

hereto.

K. r. MQELRoYQ In testimony whereof, I aliii; my signature

